As I'm trying to elevate my game, I've come across another aspect of brass prep where I have a few questions. Turn necks or ream? Why perform one operation vs the other? and when to choose one over the other? What are the pitfalls to each process?
I've searched the recent threads and have read the articles here on LRH but I don't see much on reaming the neck. Thus far I've turned necks to simply make each case with even wall thickness' by determining the thinnest point and turning almost to that thickness - about 90% of the neck turned. Doing this has made a noticable difference in the consistancy of groups. A recent batch of 20 carefully reloaded .223 fired through a chrono had an ES of 12. When I threw out the high and low shots, that ES was down to 9. This is the best I've ever been able to produce.
Anyone have experience reaming necks?
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Ream the necks when the "donut" forms where the neck begins from the shoulder. This is an "inside" ream to get concentric necks. Turn the outside for outer concentric necks. I do not ream. Have never had to do so that I'm aware of. I buy so much brass I just assume pitch a problematic case than to do more work to it.
With all due respect to Derek and Gene, I think they may have missed the key point in your question; what's the difference? Yes, reaming can be done to remove the donuts if or when they form, but that's not the primary motivation for this process. Reaming is most often performed when cases are reformed, to thin the necks down to a usable level. I don't think it sees nearly as much use these days as it has in the past for this purpose, due to better availability of "correct" brass today. This wasn't the case some years ago.
While I was in the army, I reformed virtually all of my 243 Win rounds from the tons of 7.62 NATO brass I had available to me. In necking the cases down that far, the necks were invariably far too think to allow for proper neck clearance. As a result, I had to ream the necks down to an appropriate thickness for safety reasons. The reason neck turning is still going strong is because it's an aide to accuracy, whereas reaming is (as I said) a safety/clearance issue, usually used when reforming cases . When you ream necks, you remove an equal amount of brass from all sides of that neck. In other words, if you have non-concentric necks when you begin, when the cases are reamed, you now have thinner necks that are still non-concentric. Neck turning removes neck material unevenly, taking more off the high side and less (or none) off the low side. When you're done with neck turning, you now have (hopefully) slightly thinner necks that are even, concentric and uniform, thus aiding in accuracy.
So why ream instead of just turning everything? Because it's a faster process if you're removing a lot of material. Ideally, you would ream to close to the finished thickness, then cap it off by outside turning to ensure concentricity. As I said, you don't see this as much these days, but it wasn't all that long ago that GI 30-06 brass could be had very, very cheaply, and it got made into everything from 22-250s, .243s, 25-06s, you name it. If it had a .473" head diameter, the price made it worth the extra work. Did my fair share of it then, but I'd really rather open up a box of the "proper" brass today and avoid the hassle altogether!
Donuts form at the neck-shoulder junction. If the base of your bullet does not touch the donut, it need not be removed. I no longer ream necks, but do outside turn them slightly for concistency.
This reminds me of what happened to me. I was reloading and doing min shoulder bump, and had been shooting bergers, 338, with long boattail.Then I started trying different bullets and setting, below shoulder. My sized cases where fine but once bullet seating, they where pinching, since I had the alleged donut,and my chamber was picky at that shoulder area. I ended up using several diffeent shoulder bump gauges to determine this. Reamed and not problemo
The closest I came to reaching for a reamer was with turning necked up 26wssm cases. With donut forming on necking up, and brass so thick causing excess spring back, I was challenged with turning mandrel fit.
But it was easy enough to trial & error my turner settings before necking up -with culled brass.